For a digital archive often a need exists for describing or defining the relation of the objects represented by the digital files in the archive to each other, such as whether the objects belong to each other or to groups of objects, such groups created for special purposes, or whether the object is classified according to some standard. The objects are represented by digital data in the digital files, these files called content files, that normally contain information representing a single object but can also contain information representing more than one object. Each such file containing a single object holds the information or raw digital data required for building the object, e.g. a single text, a single picture or a sound. Generally thus, the content files have contents such as the very digital data or information building texts and pictures, i.e. the digital characters representing the alphanumerical characters of texts and the digital characters representing the pixels of pictures.
In such digital archives of documents and/or pictures, sound, movies, etc. the handled entities are basically the content files themselves that contain the digital data representing text, pictures, etc. The common method of handling such digital archives and of describing the contents of the content files is to store information, herein called metadata, describing the contents of each content file in a database 101, see FIG. 1. In the database, also links, as illustrated by the lines 103, or equivalently pointers or addresses such as URLs, to the files 105 are stored, allowing the content files to be retrieved when required. Disadvantages of such database technology include that databases often are costly, require specially trained persons for maintenance and also require a high degree of discipline and accuracy of the persons maintaining the database. Thus, such traditional databases generally require costly manual work of the persons maintaining the databases and therefore, they are not widely used by private persons and families. Another disadvantage is that such technology is centralistic, i.e. the database is a central facility for all information except the very content files, and hence that the information associated with the objects is located outside the files holding the objects and hence, when the files are moved, such metadata do no automatically accompany the files in which the objects are stored. Also, as in all centralistic systems, the information flow is monodirectional, i.e. from the database towards the users who in most cases are not allowed to influence the contents of the database.
The information associated with or for objects, such metadata can include information describing or defining the relation of the objects to each other, whether objects belong to or are associated with each other or belong to groups of objects, such groups created for special purposes, or whether the object is classified according to some standard. Then, the database includes one or more tables of data and relations for objects and also of links, or equivalently of pointers or addresses, to digital files containing data representing the objects.
In the Internet or World-Wide-Web html-technology is used for maintaining the connection between database data or metadata and the files containing the data representing the texts, pictures, etc. Such technology can be considered as being contrary of conventional database technology. Information can be freely transmitted and retrieved without using any kind of hierarchical structure. However, databases are often used for supplementing Internet pages, information from the databases retrieved e.g. when a user actively selects the information. When e.g. a picture is transported by the Internet or by e-mail the content file, i.e. a graphical file, and the metadata, included in a HTML-file, are transferred separately to the computer of a user. By the Internet browser running in the user's computer the received two files are composed to form the picture that can be seen on the user's computer monitor together with text from the metadata. However, constructing HTML-files is complicated, requires special trained personnel and is therefore not often used by untrained people such as family members and office staff. A similar procedure is required in the case where all picture data is transmitted in an e-mail message.
Thus, a need has existed for technology that allows that in every file that contains e.g. graphical data or pixel data, also key information such as creator, owner, i.e. the part having the right to the picture, camera settings, information on the different objects seen in the picture. In the 1980-ies IPTC-technology started to be used for this purpose.
A few years later, the world standard format XML was created for transferring information over the Internet and similar networks. From about 2000 XML has been widely used and a plurality of XML-files, such files having the file extension .xml, exist in almost all computers of today. The company ADOBE, which is the market leader in the field of graphical computer programs, introduced the XML-technology in their commonly used portable document files, i.e. the pdf-files, and graphical files about 2001. The concept used by ADOBE is called XMP and is an open XML-application.